Essential oil
The fragrant, volatile oil within a spice, the source of most of its aroma and flavour.
Also: volatile oil, spice oil, ethereal oil, attar
Essential oils are concentrated liquids made by plants and stored in tiny glands or cells. In spices they hold most of the aroma, including eugenol in clove, cinnamaldehyde in cinnamon and carvone in caraway. Producers extract them by steam distillation or solvents. Spices are valued partly by oil content, and cardamom, cloves and nutmeg are particularly rich. Oils evaporate and oxidise, so whole spices, kept sealed and cool, hold their power far longer than powders. Concentrated oils are potent and not for casual internal use, so cooking relies on the whole spice. Essential oils also go into perfumes, soaps and industrial flavours.